/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dx.rop.cst;

/**
 * Interface for constant pools, which are, more or less, just lists of
 * {@link Constant} objects.
 */
public interface ConstantPool {

	/**
	 * Get the "size" of the constant pool. This corresponds to the class file
	 * field {@code constant_pool_count}, and is in fact always at least one
	 * more than the actual size of the constant pool, as element {@code 0} is
	 * always invalid.
	 * 
	 * @return {@code >= 1;} the size
	 */
	public int size();

	/**
	 * Get the {@code n}th entry in the constant pool, which must be valid.
	 * 
	 * @param n
	 *            {@code n >= 0, n < size();} the constant pool index
	 * @return {@code non-null;} the corresponding entry
	 * @throws IllegalArgumentException
	 *             thrown if {@code n} is in-range but invalid
	 */
	public Constant get(int n);

	/**
	 * Get the {@code n}th entry in the constant pool, which must be valid
	 * unless {@code n == 0}, in which case {@code null} is returned.
	 * 
	 * @param n
	 *            {@code n >= 0, n < size();} the constant pool index
	 * @return {@code null-ok;} the corresponding entry, if {@code n != 0}
	 * @throws IllegalArgumentException
	 *             thrown if {@code n} is in-range and non-zero but invalid
	 */
	public Constant get0Ok(int n);

	/**
	 * Get the {@code n}th entry in the constant pool, or {@code null} if the
	 * index is in-range but invalid. In particular, {@code null} is returned
	 * for index {@code 0} as well as the index after any entry which is defined
	 * to take up two slots (that is, {@code Long} and {@code Double} entries).
	 * 
	 * @param n
	 *            {@code n >= 0, n < size();} the constant pool index
	 * @return {@code null-ok;} the corresponding entry, or {@code null} if the
	 *         index is in-range but invalid
	 */
	public Constant getOrNull(int n);
}
